1. Field of the Invention
This invention relates to an improvement of a plate filter press including a number of filter plates suspended on a horizontal upper frame.
2. Description of the Prior Art
The plate filter press having suspended filter plates as above described generally comprises a chain adapted to be driven in forward and reverse directions above the filter plates. After completion of filtering, the filter plates are progressively opened one-by-one or two-by-two by a dogging mechanism secured to the chain and engageable with the respective filter plates in order to remove or drop cakes between the filter plates.
The dogging mechanism on the chain hitherto used has been so constructed to be engaged with uppermost ends of the filter plates at locations higher than slide surfaces between the filter plates and the upper frame in order to move the filter plates. During movements of the filter plates, therefore, they are likely to swing about the slide surfaces, so that there is a tendency for filter cloths extending between the filter plates to be damaged. In consideration of the swinging motion, it is necessary to provide longer distances between the filter plates than those required when the plates are opened, or to set longer time for opening the plates.
In order to avoid such disadvantages, a filter press having suspended filter plates has been proposed which comprises a plurality of slide surfaces between the upper frame and the filter plates to prevent the swinging motion of the filter plates when opening, as disclosed in U.S. Pat. No. 4,159,249 issued to Schotten. However, this filter press is complicated in construction, expensive to manufacture and difficult to maintain.
In the case of chain mechanisms of filter presses, returning distances of the chain have been controlled by means of timers in order to bring dogging means into engagement with following filter plates after completing the opening of one filter plate, as disclosed in U.S. Pat. No. 4,265,749 issued to Busse et al. Accordingly, the dogging means is prone to errors in its returned positions due to changes in speed of a motor for driving the chain. It is therefore necessary to set the returning distances longer than those required in anticipation of the errors, thereby resulting in waste time for operation and malfunctions, for example, more than a predetermined number of filter plates being inadvertently, simultaneously moved.